The present invention relates generally to induction heating systems, and more particularly to a control system to control the power to multiple zones of an induction heating coil with a bidirectional switching network.
It is well know in the induction heating field that induction heating coils have variable electrical and heating characteristics within a single coil and typically do not provide even heat distribution. Such heating coils are used to apply heat to a workpiece and such variable characteristics of the coil result in uneven heat distribution to the workpiece. It would therefore be desirable to have a system that could control individual sections or zones within a heating coil without having to physically alter the heating coil.
In other applications, certain workpieces require different heat application in different areas. Similarly, it would be desirable to alter the heat output of individual sections, or zones, within a heating coil to heat a workpiece without physically moving the workpiece with respect to the heating coil.
The simplest approach to solving this problem is to connect individual power supplies across each section of the coil. However, such an arrangement creates additional difficulties in that the sections of the coil are magnetically coupled thereby preventing accurate control. Further, magnetically isolating the sections would be expensive and result in high energy losses.
One common approach to solving this problem is to vary the distance between the coil and the workpiece. This has an effect of varying the power in that section by changing the coupling between the workpiece and the coil. However, this approach requires that the equipment be shut down while the necessary physical alterations are made to the coil. Such precise adjustments are strictly by trial and error and can take numerous attempts before the power distribution is correct, resulting in excessive down time and labor.
Therefore, it would be desirable to have an induction heating system with multi-zone control to the coil which does not require physical alteration to the coil or physical movement of the workpiece with respect to the coil that solves that aforementioned problems.